1. Field of the Invention
This invention pertains to the field of raster image systems and relates more particularly to the field of raster image systems for driving display, hardcopy or other graphical output devices such as used for displaying photographs, printing, imaging or otherwise outputting as a two-dimensional image text, diagrams, graphs and pictures.
2. Prior Art
Many imaging devices, such as television or computer monitors that include cathode ray tubes (CRT's), receive as their input a single stream of raster data and display this raster-image data in a series of lines which constitute a frame. On the other hand, some flat-panel displays, such as liquid crystal displays (LCD's), particularly the larger ones, are made of two segments, an upper segment and a lower segment, that operate in parallel and that require two parallel streams of data, one for each segment.
In the prior art, the task of generating two streams of data for use in flat-panel displays from the single stream of raster image data typically produced by controllers for CRT displays has been achieved using a frame buffer large enough to store the entire contents of one frame of data which was then read out as two streams of data. Examples of such prior art are chips for video-to-LCD conversion such as the SED 1341 F.sub.OE and the SED 1345 F.sub.OA, both from SMOS Systems, Inc. (Technical Manual SED 1341 F.sub.OE, 1988 and Technical Manual SED 1345 F.sub.OA, SMOS Systems, Inc., 2460 North First Street, San Jose, Calif. 95131). Both of these chips require a minimum of one bit of data for each pixel in the frame. For example, the chip SED 1341 F.sub.OE requires 40K bytes of memory to work with 640 times 480 display (Page 38, Technical Reference Manual SED 1341 F.sub.OE). An example of a suitable LCD for use in the present invention is the model LM640487Z sold by the Elecom Group of the Sharp Corporation.
In producing an image on an imaging device, there is often a need for centering the image to be displayed (or otherwise input), on the imaging device. In the prior art, centering of an image on the imaging device required altering the characteristics of raster data from the source or the use of flexible imaging devices, such as CRT's with multisync capabilities. Currently available flat panel displays, such as LCD's, have no such flexibility. In the prior art, the control of image position was dependent on ensuring the proper positioning of horizontal and vertical synchronization signals.